In the Japanese Published Unexamined Application No. 112856 of 1998, there is disclosed an image transmitter adapted to send image data in an area in an image in an amount of information and image data in another area in another amount of information from a sending side to a receiving side as designated by the receiving side. With the image transmitter disclosed in the Japanese Published Unexamined Application No. 112856 of 1998, it is possible to display an image of a specific area including designated points at a high spatial resolution and images other areas at low spatial resolutions.
More particularly, in case image data are sent from the sending side to receiving side via a transmission line, it is not possible to send image data whose data rate exceeds the transmission rate of the transmission line. Therefore, for real-time display of an image at the receiving side, image data have to be sent from the sending side to receiving side at a data rate lower than the transmission rate of the transmission line. As a result, if the transmission rate is not sufficient, all images will be displayed at the receiving side at lower spatial resolutions.
On the other hand, by permitting to send image data in an area in an image in an amount of information and image data in other areas in the image in another amount of information as in the image transmitter disclosed in the Japanese Published Unexamined Application No.112856 of 1998 and sending image data in a specific area including points designated by the receiving side in an increased amount of information and image data in other areas in a decreased amount of information, it is possible to display the image of the specific area including the points designated by the receiving side at a high spatial resolution and the images of other areas at a low spatial resolution. Thus, it is possible to display an image area the user wants to view in detail at a high spatial resolution while displaying other image areas at a low spatial resolution. That is, with the image transmitter disclosed in the Japanese Published Unexamined Application No. 112856 of 1998, it is possible to display an image area the user desires to view in detail at an improved spatial resolution at the sacrifice of the spatial resolution of the other areas.
Also, in the PCT Published Unexamined Application No. WO01/1189A1 of the Applicant of the present invention, there is disclosed an image processor adapted to effect the spatial resolution control as disclosed in the Japanese Published Unexamined Application No. 112856 of 1998 as well as the time resolution control in order to control the amount of information in an area designated at the receiving side. Further, the above PCT Published Unexamined Application No. WO01/1189A1 discloses an image processor adapted to extract object images from image data sent from the sending side to receiving side by judging, based on a position clicked with the mouse by the user at the receiving side and time interval between clicks, whether an image in the clicked position is moving or stationary and also whether the clicks are temporally successive.
It should be reminded here that to improve the spatial resolution of for example an image area (will be referred to as “interesting area” wherever appropriate hereunder) the user takes interest in seeing in detail and reduce the spatial resolution of other image areas such as background for example, it is necessary at the sending side to localize an image area the user at the receiving side, that is, an interesting area.
As in the above, if an area the user at the receiving side is interested in can be localized, it is possible when sending image data from the sending side to the receiving side to send an increased amount of image data in the interesting area.
The PCT Published Unexamined Application No. WO01-1189A1 discloses also a method for localizing an area the user is interested in as designated in a received image data by clicking the mouse or the like at the receiving side, for example, a method for extracting object images for example. In this method, however, since any object image is not reviewed, so there is a problem that objects which are extracted as object images at a time and which is uncoupled as another object image will always be handled as belonging to the same object.
Further, in case the user's interest shifts from one area to another image area, it is necessary to detect the shift of the user's interest and localize an image area the user is currently interested in. That is, processing of image data based on existing information after the user's interest has shifted to another image area, will possibly lead to a misjudgement. Therefore, in case the user's interest has shifted to another image area, the shift has to be detected for changing the manner of image data processing.